What is the lowest number of users I can have for my app (in respect to billing purposes) plan?

The Quick Base plans are more based on features and not the # of users.

The plans are listed here, but I have found that for all of my clients, they need the middle level plan "Premier" to get the feature set we need.  The entry level plan is missing some important features.

http://www.quickbase.com/plans-and-pricing